Impending condensation alarm

ABSTRACT

Device for warning of impending condensation including a sensor in contact with the element being monitored to measure conductivity at the sensor, an alarm, and electrical circuitry responding to the sensor to trigger the alarm at a given temperature above dew point.

United States Patent 3,696,360 ,Gajewski [4 Oct. 3, 1972 [54] IMPENDINGCONDENSATION ALARM 2,733,607 2/1956 Miller ..73/336.5 72 I I I I G ki IIII. 2,904,995 9/1959 Obermaier ..340/235 1 aw News 3,293,901 12/1966Scoyoc et a] ..73/17 A [73] Assigneez Vapor Corporation, Chicago, 111.Filed: June 1971 FOREIGN PATENTS OR AIPPILICATIONS pp No: 153,614900,194 7/1962 Great Britaln ..340/235 Primary Examiner-John W. Caldwell[52] US. Cl ..340/235, 73/17 A, 73/336.5, A i an Ex m ner-Scott F Prtridge 324/65 R Attorney-Julian Falk et al. [51] Int. Cl. ..G0ln 25/00[58] Field of Search....340/235, 228; 73/17 A, 336.5; [57] ABSTRACT I324/65 Device for warning of impending condensation including a sensorin contact with the element being moni- [56] References cued tored tomeasure conductivity at the sensor, an alarm, UNITED STATES PATENTS andelectrical circuitry responding to the sensor to trigger the alarm at agiven temperature above dew 3,422,677 1/1969 Lockwood ..73/336.5 point3,416,356 12/1968 Bridgeman ..73/17 A 3,599,862 8/1971 Hogan ..340/235 X5 Claims, 3 Drawing Figures 3 n I L I IZ Z T II 31 34 I l I 61 65 1 T 1I 36 l I 63 1 l I I I I 46 I I I 48 I LZ 64 so 62 4I I 37 40 I I 47 I 3839 1 49 I I L -l 1 PATENTEUUBT 3 I972 TRANS)STOR SWITC H MULTIVI BRATORALA RM POWER 5U P P LY VOLTAGE DOUBLER & RECTIFIER SENSOR OPERATIONALAMPLIFIER CIRCUDT INVENTOR WIESLAW GAJEWSKI 5% rim IMPENDINGCONDENSATION ALARM This invention relates in general to a device formonitoring an element and the atmosphere in which the element is placedto warn of impending condensation conditions that would be injurious tothe element so that steps can be taken to avoid the impendingcondensation conditions, and more particularly to a device that isextremely compact and operable on a minimum amount of electrical powerto warn of impending dew point temperature.

The advent of the present invention follows a searching need in industryfor an impending condensation alarm to provide advance warning ofcondensation. Heretofore, many different types of dew point hygrometershave been developed, such as in U. S. No. 3,416,356, and which include asensor that measures conductivity of a gaseous environment in whichmeasurement is desired. However, a suitable cooling means has alwaysbeen provided for driving the sensor, and as such, the hygrometer hasbeen bulky and costly. Moreover, the hygrometers heretofore developedhave utilized expensive readout arrangements to visually read out dewpoint temperature.

The present invention, answering the need for a compact and inexpensiveimpending condensation alarm, includes a sensor having spaced conductorsin the form of a grid intimately mounted on an insulator which is inphysical contact with the element being monitored. The temperature ofthe sensor therefore follows the temperature of the element beingmonitored, while the conductivity of the insulator surface is measuredby the grid to describe the relationship of the temperature of thesensor surface to the dew point temperature The size of the sensor issmall, on the order of inch in diameter, to minimize thermal gradientsand to facilitate its usage in small confined areas as well as largeareas. The sensor is electrically connected to a circuit on a printedcircuit board that is about 2 inches square and which includes amultivibrator to apply an alternating current bias to the sensor, anintegrated circuit operational amplifier receiving the signal voltage ofthe sensor, and a voltage doubler and rectifier receiving the output ofthe amplifier. A transistor switch responsive to the voltage signal ofthe voltage doubler and rectifier is connected to an alarm which ittriggers at a given voltage level. The resistance of the sensor grid isproportional to the absolute difference between the sensor temperatureand dew point temperature. The sensor is mounted on a small metal basefor rigidity and to enhance thermal transfer to the sensor from thesurface or atmosphere being monitored. The sensor is adaptable for usein measuring impending condensation in a variety of situations, such asthe atmosphere, cold water pipes, and the ground.

It is, therefore, an object of the present invention to provide a uniqueand compact impending condensation alarm.

Another object of this invention is in the provision of an impendingcondensation alarm that is compact and economical to manufacture, andwhich operates pursuant to a minimum amount of electrical power, andwhich is capable of use in measuring impending condensation for avariety of situations.

Other objects, features and advantages of the invention will be apparentfrom the following detailed disclosure, taken in conjunction with theaccompanying sheets of drawings, wherein like reference numerals referto like parts, in which:

FIG. 1 is a block diagram of the impending condensation alarm accordingto the invention;

FIG. 2 is an electrical, schematic diagram of the circuitry employed ona printed circuit board to provide a voltage signal for operating atransistor switch; and

FIG. 3 is a front, perspective view of the sensor according to theinvention mounted on a metal base.

Referring now to the drawings, and particularly to FIG. 1, the impendingcondensation alarm of the invention includes a sensor 10, having appliedthereto an alternating current bias by a multivibrator 11. The voltageoutput of the sensor is received by an integrated circuit operationalamplifier 12, and the output from the amplifier is delivered to avoltage doubler and rectifier 13. A transistor switch 14 is connected tothe output of the voltage doubler and rectifier, and which is triggeredwhen the voltage reaches a certain level to energize an alarm 15. Thealarm may be of any suitable type, such as a device for emitting anaudible signal, a light, a heater control for energizing a heater, acontrol for energizing dehumidifying equipment, a relay or other. Apower supply 16 is connected to the multivibrator 11, the operationalamplifier 12, the voltage doubler and rectifier 13, the transistorswitch 14, and the alarm 15. The power supply may be in the form ofbatteries or line voltage, and inasmuch as the components of thecircuitry are solid state, a minimum amount of electrical power isneeded.

The sensor 10 includes a pair of spaced conductors on an insulator, theconductivity of the insulator surface describing the relationship of thesurface of the dew point temperature. The resistance of the surface, asmeasured by the spaced conductors, is proportional to the absolutedifference between sensor temperature and dew point temperature, whichis reflected in the voltage signal delivered to the operationalamplifier 12.

The sensor 10, FIG. 3, which is adapted to follow the temperature of theelement being monitored includes a disc 20 of insulating material, suchas epoxy fiberglass board, and firstand second spaced conductors 21 and22 on the upper surface of the board in intimate contact therewith. Thiscould be fabricated by printed circuit techniques. Each of theconductors include a plurality of conductor fingers interjacentlyarranged with eaCh other to form a grid-like arrangement. Thus,conductivity on the surface of the board 20 is measured between thefinger conductors. A lead-in wire 23 is provided for the conductor 21,while the lead-in wire 24 is provided for the conductor 22. Thematerials employed for the conductors 21 and 22 are their respectivelead-in wires are not of material consequence, although it is preferredthat they be copper clad with an inert metal, such as a noble metal. Theunder surface of the board 20 is mounted on a metal base 25 which provides rigidity for the board 20 and also serves as a thermal transferelement between the element being monitored and the board 20. Forexample, the base 20 may be used to respond to atmosphere or may bemounted directly against an element being monitored, and in the latterevent, it may be shaped to provide intimate con tact with the element.

The sensor 10 has applied thereto an alternating current biased by amultivibrator of any suitable type, any

one of which is satisfactory, as shown in FIG. 2. The multivibrator 11includes first and second transistors 30 and 31. A resistor 33 isconnected between the base and emitter, while a resistor 34 is connectedbetween the base and emitter of transistor 31. A capacitor 35 isconnected between the base of transistor 30 and the collector oftransistor 31, while a capacitor 36 is connected between the base oftransistor 31 and the collector of transistor 30. Resistors 37 and 38are connected between the base and collector of transistor 30, whileresistors 39 and 40 are connected between the base and collector oftransistor 31. The conductor 21 of the sensor is connected to themultivibrator through a coupling capacitor 41, while the conductor 22 isconnected to ground through resistor 42.

In the operational amplifier circuit, an integrated circuit operationalamplifier 45 includes inputs 46 and 47, and output 48, and power inputs49 and 50. The input 46 is connected to ground through resistor 51,while the input 47 is connected to the conductor 22 of the sensor 10.The power supply includes 9 volt batteries 52 and 53 connected inseries, and their common being connected to ground, while the batteriesare connected to the power outputs 49 and 50 of the operationalamplifier 45. The multivibrator is connected to the batteries throughline 54. A resistor 55 is connected between the input 46 and output 48of the operational amplifier to provide feed-back, and the output 48 isconnected to the voltage doubler and rectifier 13.

The voltage doubler and rectifier 13 includes diodes 60 and 61, andcapacitors 62 and 63, and output taps 64 and 65, the latter of whichwould be connected to the transistor switch 14. Any suitable transistorswitch may be employed which would be triggered when the voltage signalfrom the taps 64 and 65 reaches a given level.

In operation, when the voltage level at the output of the voltagedoubler and rectifier reaches a given value indicating impendingcondensation of the element being monitored, the element would beenergized, it being appreciated that the resistance of the grid on thesensor 10 is proportional to the absolute difference between the sensortemperature and the dew point temperature.

The types and values of the following components have provedsatisfactory.

2N 3566 SH CE Diodes 60,61 1N 914 Sensor Grid 10 Vap-Air PIN 2683 9691Resistors 37, 39 K i 10%, %W, Carbon Resistors 33, 34 22K 1 10%, 54W,Carbon Resistors 38, 40 3.3K 10%, AW, Carbon Resistor 42 220K 1' l0%,V4W, Carbon Resistor 51 2.2K 10%, AW, Carbon Resistor 55 33K 10%. AW,Carbon Capacitors 35, 41, 36 .l mf, 100 VDC Capacitors 62, 63 10 mt, 10VDC It will 'be understood that modifications and variations may beeffected without departing from the scope of the novel concepts of thepresent invention, but it is understood that this application is to belimited only by the scope of the appended claims.

The invention is hereby claimed as follows:

1. An impending condensation alarm comprising, a sensor adapted to be incontact with the element being monitored, sai sensor including aninsulating board having a pair 0 spaced conductors int1mately mounted onone surface and exposed to ambient air, the other surface of said boardbeing in contact with the element being monitored, an alarm, electricalcircuit means measuring the conductivity of the insulating board surfacethrough the spaced conductors to describe the relationship of thetemperature of the one surface to the dew point temperature and totrigger the alarm when the resistance between the spaced conductorsreaches a given value warning of impending condensation.

2. The combination of claim 1, and a metal support upon which the boardis mounted to rigidify same and to contact directly the element beingmonitored, thereby also providing a thermal conductor between the boardand element being monitored.

3. The combination of claim 1, wherein said electrical circuit meansincludes a multivibrator connected to the spaced conductors to apply analternating current bias thereto, an operational amplifier receiving theout put from the sensor, and a voltage doubler and rectifier receivingthe output from the operational amplifier.

4. The combination of claim 1, wherein said spaced conductors include aplurality of conductor fingers spaced from each other such that theconductor fingers of one of the spaced conductors are interjacentlyarranged with the finger conductors of the other of the spacedconductors to define a grid.

5. The combination of claim 4, and a transistor switch between the alarmand the voltage doubler triggering when the voltage output of saidvoltage doubler reaches a given level.

1. An impending condensation alarm comprising, a sensor adapted to be incontact with the element being monitored, said sensor including aninsulating board having a pair of spaced conductors intimately mountedon one surface and exposed to ambient air, the other surface of saidboard being in contact with the element being monitored, an alarm,electrical circuit means measuring the conductivity of the insulatingboard surface through the spaced conductors to describe the relationshipof the temperature of the one surface to the dew point temperature andto trigger the alarm when the resistance between the spaced conductorsreaches a given value warning of impending condensation.
 2. Thecombination of claim 1, and a metal support upon which the board ismounted to rigidify same and to contact directly the element beingmonitored, thereby also providing a thermal conductor between the boardand element being monitored.
 3. The combination of claim 1, wherein saidelectrical circuit means includes a multivibrator connected to thespaced conductors to apply an alternating current bias thereto, anoperational amplifier receiving the output from the sensor, and avoltage doubler and rectifier receiving the output from the operationalamplifier.
 4. The combination of claim 1, wherein said spaced conductorsinclude a plurality of conductor fingers spaced from each other suchthat the conductor fingers of one of the spaced conductors areinterjacently arranged with the finger conductors of the other of thespaced conductors to define a grid.
 5. The combination of claim 4, and atransistor switch between the alarm and the voltage doubler triggeringwhen the voltage output of said voltage doubler reaches a given level.